In a typical paint-making process, a dispersant is added in the grinding stage to help pigments and extenders to stably disperse. Polyacid homopolymers or copolymers are commonly used as dispersants. In the same grinding stage, thickeners are added to provide high enough viscosity to grind pigment/extender to fine sizes, as well as to deliver the proper viscosity for the final paint. Thickeners used in grinding stage, typically, are Hydroxyethyl Cellulose (HEC). In the letdown stage, more thickeners are added to reach the target viscosity for the final paint. In economy paint space, HEC and polyacid dispersant are added in the grinding stage to deliver dispersion and viscosity, and minimal thickeners could be added in the letdown stage to reach the target viscosity.
In the effort of replacing HEC for cost saving and better flow/leveling, Hydrophobically-modified Alkali Soluble Emulsion (HASE) was added in the letdown stage to reach the target viscosity. However, this approach will make the paint film more hydrophilic and lead to significant loss on scrub resistance (washability). To make the paint film more hydrophobic, hydrophobic copolymer dispersant can be used to replace the polyacid dispersant in the grinding stage. However, the combination of hydrophobic dispersant with HASE provides insufficient dispersion of pigment in a painting composition as well as decreased long term viscosity stability.
Some grinding additives are used in a paint formulation such as U.S. Pat. Nos. 8,883,880B, 8,158,714B, EP1302515, AU2014200431, WO2014/040290A and U.S. Pat. No. 5,266,646. But it is still desirable to paint formulators a compatible composition of HASE and hydrophobic dispersant, which will provide improved dispersion of pigment in a painting composition as well as long term viscosity stability.